1. Field of the Invention
The present invention relates to a conductive glass-lining composition for glass-lined equipment, using as a base material, low carbon steel plate or stainless steel plate that can withstand severe service conditions in the chemical industry, medical industry, food industry, etc.
2. Description of the Related Art
Conventional glass lining equipment has been produced by stoving a ground coat glaze with a thickness of approximately 0.2 to 0.4 mm on a base material such as low carbon steel plate or stainless steel plate so as to adhere the ground coat glaze strongly to the base material, and then by stoving a cover coat glaze having high corrosion resistance normally in a thickness of 0.8 to 2.0 mm.
Since the glass lining material that constitutes in the glass lined equipment is an insulating material having a volume resistivity of approximately 1.times.10.sup.13 to 10.sup.14 .OMEGA.cm, if the glass lining equipment is operated and agitated using a non-aqueous organic liquid, the amount of electrified charge becomes much larger than that of the leak charge, generating tens or hundreds of thousands volts of static electricity, which may cause breakage or explosion of the glass lining material even if the glass lined equipment is grounded.
To prevent the above problems, when the glass lined equipment is operated to agitate non-aqueous organic liquid, Ta metal chips are embedded in a glass lining layer in advance or Ta metal wires are wound around the surface of a baffle or the like. However, it is difficult to coat the full surface of the glass lining with Ta metal, so no sufficient countermeasures for the static electricity have yet been reached. Furthermore, where the production of a great amount of the static electricity is predicted, metal equipment such as of stainless steel is used instead of glass lined equipment.
As an example of glass lined equipment having antistatic means, Japanese Utility Model Laid-Open No. 7-28834 discloses a glass lined metallic can where the inside walls thereof are covered with an under glass coating layer with an upper glass coating layer coated thereon wherein the upper glass is made of conductive glass embedded with platinum wire which is connected to the base material of the metallic can. However, the portion not embedded with platinum wire can not be expected to have much antistatic properties of the glass lining.
Further, Japanese Patent Publication No. 60-25380 discloses a method for fabricating a glass lined product by adding inorganic fibers 0.1 to 3 mm in length to a frit strip having a predetermined glass composition in which 2 to 10 percent of the fibers is added to 100 percent of the strip, and by glazing with a spray gun or in a immersion bath. The inorganic fibers exemplified in this Publication are materials that have been fiberized from glass having a different composition than enamel type glass or from commercial glass; natural mineral fibers such as rock fibers and kaowool; artificial ceramic fibers or whiskers such as zirconia, alumina, chromium oxide or the like. The object of adding the fibers is to reduce air bubbles in the enamel product, to prevent giant bubbles, and to improve color spot resistance, glazing crack (fissure) resistance, thermal shock resistance and mechanical shock resistance.
Japanese Patent Publication No. 4-8390 discloses a glaze composition including a frit wherein the glaze composition includes 100 parts by weight of the frit and 20 to 100 parts by weight of inorganic whiskers having diameters of 0.2 to 1 .mu.m and a length-to-diameter ratio of not less than 20. The whiskers are inorganic single crystal fibers selected from the group consisting of titania, potassium titanate, alumina, silicon carbide and silicon nitride. The object of adding the whiskers is to import cutting machinability to the glass lining and to improve wear resistance.
Accordingly, an object of the present invention is to provide a conductive glass lining composition capable of providing a conductive glass lining showing excellent volume resistivity.